The invention relates to microwave power amplifiers and, in particular, L-Band microwave transistor power amplifiers with a dynamically efficient biasing arrangement and having application in multiple beam phased antenna arrays.
In an active multiple beam phased antenna array system each antenna element (or elemental sub-array) is driven by a dedicated power amplifier. A requirement of such a system is that the power can be flexibly reallocated between different beams and that the power amplifiers have to be capable of operation over a wide dynamic range whilst simultaneously maintaining a very high degree of gain and phase tracking.
In order to maintain reasonable high levels of efficiency in phase array systems it is necessary to operate amplifiers in their non-linear regions. Additionally, to provide for a wide signal dynamic (20 dB minimum) the most efficient bias modes (Class B or C) are not normally contemplated, instead the designer resorts to "overrun" Class A amplifiers (Class A/B).
It is an object of the present invention to provide a power amplifier with dynamically efficient biasing and capable of linear operation whilst under effective Class B (non-linear) bias.